The candidate is a physician-epidemiologist who focuses on the interaction of environmental factors, specifically viral infections in early childhood, and how they contribute to the development of asthma. The candidate will increase her knowledge of asthma, atopy, and epidemiology by attending courses in immunology, microbiology and epidemiology, and by attending clinical conferences. The candidate will conduct the proposed research under the guidance of mentors and an advisory committee who have expertise in all areas related to the project. The goals of this proposal are to train the candidate to do prospective and retrospective epidemiologic investigations, and specifically to investigate the role of bronchiolitis during infancy and the development of asthma. Observational studies have reported that over 30% of hospitalized infants with Respiratory Syncytial Virus (RSV) bronchiolitis subsequently develop asthma. However, it is not known whether the severity or viral etiology of bronchiolitis is associated with increased asthma risk. Neither is it known how two risk factors for asthma, familial predisposition to develop asthma and environmental tobacco smoke [ETS], interact with bronchiolitis to affect asthma risk. The candidate will test the hypothesis that (a) clinically significant bronchiolitis of any severity is associated with increased risk of developing asthma, with more severe bronchiolitis associated with greater asthma risk and that (b) RSV vs. non-RSV respiratory viruses confer different risks on the development of childhood asthma, and that (c) familial-environment interactions modify the risk of developing asthma. In Specific Aim #1, the candidate will conduct a retrospective population-based cohort study using Tennessee Medicaid data to determine the association of bronchiolitis of RSV and non-RSV etiology, including inpatient and outpatient care, with asthma at age 5 years. In Specific Aim #2, the candidate will extend follow-up to age 5 years of an ongoing prospective cohort (Atopy-Bronchiolitis Cohort) of infants with either a hospitalization or outpatient visit for bronchiolitis during infancy to determine whether viral etiology and bronchiolitis severity are independently associated with asthma development. Findings will identify infants who are at the greatest risk for developing asthma, what modifiable factors interact with bronchiolitis to increase the risk, and thus guide the future application and evaluation of preventive or treatment measures during infancy.